The present invention relates to a method of detecting an end point of a process such as a manufacture process and a test process, a device to be used in the method, a computer memory product in which a computer program for executing the method is stored, and a chemical mechanical polishing apparatus provided with the device for detecting an end point of a process.
In the case where a semiconductor device such as a LSI and a VLSI is to be manufactured by using a wafer in which plural films are stacked on a silicon substrate, it is necessary to planarize the film surface of a desired layer in order to realize the higher circuit integration of the semiconductor device. The usage of a chemical mechanical polishing (hereinafter refereed to as the CMP) apparatus has been proposed for this purpose.
In a CMP apparatus, a polishing cloth impregnated with a polishing solution such as an alkaline colloidal silica solution is allowed to be in contact with the surface of a wafer with an appropriate force applied, and the polishing cloth is driven to be rotated, so that the film surface of the wafer can be planarized through composite functions of chemical etching using the alkaline solution and mechanical polishing using the colloidal silica. The end point of the polishing process by using the CMP apparatus has been conventionally detected by repeatedly measuring the thickness of the film with the CMP apparatus temporarily halted. Therefore, it disadvantageously takes a long time to planarize plural wafers. Accordingly, Japanese Patent Application Laid-Open No. 8-306648 (1996) discloses the following apparatus as a countermeasure.
FIG. 1 is a block diagram for showing the structure of an end point detector disclosed in Japanese Patent Application Laid Open No. 8-306648 together with the structure of a CMP apparatus. In FIG. 1, a reference numeral 32 denotes a polishing table in the shape of a bottomed cylinder. A polishing cloth 31 impregnated with a polishing solution is stretched over the opening of the polishing table 32, so as to be in contact with the surface of a wafer W in which plural films are stacked on a silicon substrate. At the center of the bottom of the polishing table 32, the output axis of a DC motor 34 is vertically provided. The DC motor 34 has power terminals 35 and 36, with the power terminal 36 connected with a positive terminal of a power supply 37 and the power terminal 35 connected with a negative terminal of the power supply 37 through a switch 38.
The power terminals 35 and 36 of the-DC motor 34 are also connected with an analyzer 41 for analyzing a frequency characteristic of an electric signal. The analyzer 41 analyzes a frequency characteristic of a noise signal appearing at the power terminals 35 and 36 of the DC motor 34, and supplies a result of the analysis to a level discriminating circuit 42. In the noise signal, different frequency components appear in accordance with the materials of the respective films of the wafer W.
In the level discriminating circuit 42, specific frequency components appearing in polishing the respective films of the wafer W by the CMP apparatus are previously set. The level discriminating circuit 42 generates time series data at levels of the specific frequency components on the basis of the results of the analysis supplied with time by the analyzer 41, detects the timing of a peak in the generated time series data, and supplies a peak detection signal to a control circuit 39. The control circuit 39 turns the switch 38 on in response to the peak detection signal, thereby halting the polishing of the wafer W by the CMP apparatus.
In the end point detector described in Japanese Patent Application Laid-Open No. 8-306648, however, the analysis of the frequency characteristic takes a long time because the frequency characteristic of the noise signal appearing at the power terminals of the DC motor is analyzed by the analyzer. Therefore, there arises a problem that the polishing speed of the CMP apparatus should be set low. Furthermore, it is necessary to previously determine the specific frequencies corresponding to the materials of plural films through tests to be previously set in the level discriminating circuit, which is disadvantageously troublesome. In addition, the analyzer for analyzing the frequency characteristic is disadvantageously expensive.